Process for the preparation of laminates

ABSTRACT

The process comprises the steps
 i) production of one layer by bringing a fibrous support material into contact with a curable mixture containing an epoxy resin having an average of at least two 1,2-epoxide groups per molecule or a mixture of these epoxy resins and a compound of the formula I or a mixture of these compounds 
&lt;IMAGE&gt;
 in which a and b, independently of one another, are 1 or 2, R&lt;1&gt; is a  pi -arene, R&lt;2&gt; is a  pi -arene or an indenyl or cyclopentadienyl anion, X&lt;-&gt; is an anion [LQm]&lt;-&gt; or an anion of a partially or perfluorinated aliphatic or aromatic sulphonic acid, L is P, As or Sb, Q is fluorine, or some of the radicals Q may alternatively be hydroxyl groups, and m corresponds to the valency of L increased by one,
 ii) production of a layer sequence comprising at least two layer-form materials to be bonded to one another, of which at least one is a layer obtainable in accordance with step i) in which the curable material is essentially in unchanged form, and
 iii) pressing said layer sequence at elevated temperature, the pressure and temperature being selected in such a manner that a liquid matrix resin is present at the beginning of this step, a drop in viscosity takes place initially so that virtually all included gases can escape from the layer sequence, and the increase in viscosity during the subsequent crosslinking reaction takes place so rapidly that the resin flowing out does not stick the compression mould together. 
&lt;??&gt;The laminates obtainable in accordance with the invention are suitable for the production of circuit boards and insulation materials.

This is a divisional of application Ser. No. 279,747 filed on Dec. 5,1988 now U.S. Pat. No. 4,963,300.

The invention relates to a process for the preparation of laminates, theproducts obtainable from said process and the use of particular curingagents for the preparation of laminates.

Cationically curable mixtures containing metallocene complex salts asinitiators are disclosed in EP A 94,915.

Selected curing agent/accelerator combinations, for example thedicyanediamide/benzyldimethylamine combination, are generally used forthe preparation of laminates based on epoxides.

The resin formulations must meet a range of requirements, some which aredifficult to reconcile.

Thus, for example, the prepreg should have an adequate shelf life, whilethe resin matrix in the compression mould should have a fast cure.Moreover the viscosity of the resin matrix should fall, at the beginningof the compression moulding process, to allow gases contained within thematerial to be pressed to escape. However, the fall in viscosity shouldonly be to the extent which ensures that only a small proportion of theresin flows out of the fibre matrix.

Generally in hitherto known processes the crosslinking reaction beginsas early as the prepreg preparation stage, since the disclosed curingagent/accelerator combinations already enter into a certain chemicalreaction with the epoxy resin. Thus in the compression moulding processpressure and temperature must be altered in accordance with the reactionmentioned, in order to obtain the desired viscosity profile in the resinmatrix.

A process for the preparation of laminates has now been found in whichthe pressure and temperature profiles in the compression moulding stepcan be varied within wide limits and in which shorter compressionmoulding cycles may be used compared with conventional processes.Moreover this process surprisingly produces laminates with improvedfinal properties, such as increased glass transition temperature of theresin matrix or lower solvent absorbency in the laminate.

In this process a resin/initiator combination having a long latentperiod is used, with which the processing conditions can be adjusted insuch a way that practically no preliminary crosslinking occurs duringthe prepreg preparation stage.

The process is further based on the surprising finding, that the curingreaction begins quickly and is completed rapidly in the compressionstep. Low viscosities of the matrix resin can thus be used at thebeginning of the compression moulding process and the process may becontrolled in such a way that only a desired proportion of the resinflows out of the fibre matrix.

The present invention relates to a process for the preparation of alaminate comprising the steps

i) preparation of a layer by bringing into contact a fibrous substratewith a curable mixture containing an epoxy resin having on average atleast two 1,2-epoxide groups per molecule or a mixture of these epoxyresins and a compound of the formula I

    [R.sup.1 (Fe.sup.II R.sup.2).sub.a ].sup.ab⊕ ab.[X].sup.⊖(I)

or a mixture of these compounds, in which a and b are independent of oneanother 1 or 2, R¹ is a π-arene, R² is a π-arene or an indenyl-orcyclopentadienyl anion, X⁻ is an anion [LQ_(m) ]⁻ or an anion of apartly fluorinated or perflourinated aliphatic or aromatic sulfonicacid, L is P, As or Sb, Q is fluorine or some of the Q substituents mayalso be hydroxyl groups, and m corresponds to a value which exceeds thevalence of L by unity,

ii) preparation of a laminated sequence from at least two layeredmaterials which are to be bonded together, at least one of which is alayer which is obtainable according to step i), in which the curablematerial is essentially present in its unaltered state, and

iii) compression moulding of the said laminate sequence at elevatedtemperature, in which pressure and temperature are selected in such away that a liquid resin matrix is present at the beginning of this step,in which an initial fall in the viscosity is produced, so that entrainedgases can virtually entirely escape from the laminate sequence, and thatin the subsequent crosslinking reaction the rise in viscosity is carriedout so quickly that the resin which flows out does not bind thecompression mould.

In principle, all fibres which can form a bond with the epoxide matrixand produce a reinforcement of the matrix material are suitable assubstrates.

Examples of fibre materials are natural polymers, such as cellulose;metals, such as steel, Ti, W, Ta or Mo; organic fibre-forming polymers,particularly aromatic polyamides, such as Nomex or Kevlar; carbon, forexample materials prepared by carbonizing cellulose, polyacrylonitrileor pitch; and particularly glass.

The fibre materials can be used as substrates in the most varied forms.They may be used for example in the form of continuous threads(individual-filaments or spun yarns), continuous filament yarns, orparallel rovings, as woven continuous filament yarns, spun rovings,roving fabrics, chopped fibres, continuous filament mats, chopped strandmats, webs, or felts (papers).

The bringing into contact of the fibrous substrate and the curablemixture will be different depending on the type of fibre and the shapeof fibre or the properties of the matrix material. Examples of suchprocesses are the impregnation of woven fabrics, non woven or continuousfibres with the liquid resin-initiator mixture or with a solution of asolid resin/initiator mixture in an inert solvent.

Layers containing chopped fibres can for example be prepared byspreading the curable mixture together with cut fibres on a fabric or ametal foil.

The bringing into contact of the fibrous substrate with the curablemixture is preferably carried out by impregnation. For this purpose websof the said substrate are for example passed through a resin bath,containing epoxy resin, the initiator and, if appropriate, a solvent,are dried if desired, and subsequently wound up onto a storage spool.

It is recommended that the impregnated layers are subjected to a lightexposure step before step ii). The compound of formula I is thusconverted into an activated form. This treatment enables the subsequenthot cure to be carried out at lower temperatures than would be requiredin the case of direct hot curing.

A process is thus preferred which comprises the steps i), ii) and iii),defined above and in which an irradiation step ia) is also incorporatedprior to step ii), in which the compound of formula I is activated byexposure to actinic radiation.

In this case the prepreg obtained in step i) may be irradiated or afibrous substrate may be impregnated with a previously irradiatedmixture of epoxy resin and initiator of the formula I.

The intensity and wavelength of the radiation to be used is dependent onthe type of initiator; depending on the nature of the arene ligand R¹the absorption of the initiator may vary within the UV range or withinthe visible range, for example in the 250-600 nm range.

Depending on the nature of the initiator, the curable mixture mayadditionally contain a sensitizer for the said initiator. Moreover thecurable mixture may contain combinations of compounds of the formula Iwith oxidizing agents. These embodiments are described in EP A 152,377and EP A 126,712. The descriptions of these publications are likewise asubject of the present description.

After impregnation and exposure to light, the material mayadvantageously be heated briefly, for example to 70°-120° C., in orderto increase the viscosity of the resin, before step ii) is carried out.

In step ii) individual layers of the previously obtained material arelaid on top of one another in the desired number. In this case thelayers may all be of the same material or layers of other materials mayalso be present.

Examples of layers of other materials are metal foils, such as copperfoils or aluminium foils, or other reinforcements, such as mats ornonwovens made from fibrous reinforcing material.

In step iii) the arrangement arrived at according to step ii) is curedby compression moulding and heating.

The process conditions in step iii) may be held constant or varied. Inan initial stage, for example, pressure and temperature can be appliedin such a way that essentially no curing occurs or the speed of cure isso slow that the resin viscosity falls to the desired value as a resultof the temperature increase. Subsequently pressure and/or temperaturecan be increased, so that the desired rate of increase in viscosity isattained. These increases can be carried out continuously or in stages.The pressure can also, for example, be increased in stages in accordancewith the increase in viscosity, while the temperature is continuouslyincreased.

Pressure and temperature can also, however, be present immediately atthe beginning of step iii), so that the crosslinking reaction beginsvirtually immediately. This procedure is recommended in the case ofliquid matrix resins having low viscosity. Here in general the initialcompression is sufficient to remove the entrained gases from the layeredmaterial. Generally in systems of this kind there is only a short dropin viscosity before the curing reaction brings about an increase inviscosity.

Step iii) can be carried out discontinuously in multiple-daylightpresses or continuously in twin belt presses.

In a preferred embodiment of the process steps ii) and iii) are carriedout continuously. For this purpose, webs of the material obtainableaccording to step i) if desired, together with webs of other materialsin layered form to be bonded together, are, for example, fedsimultaneously between heatable twin belt presses in the particulardesired lamination sequence.

In this embodiment, step i) can be carried out separately, by which thefibrous substrate is brought into contact with the curable mixture andthe webs obtained are wound up on storage spools.

Step i) can, however, also be carried out continuously together withsteps ii) and iii), by which, for example, webs of the fibrous substrateare fed through a resin bath immediately before step ii).

In the continuous procedure, particularly fast acting initiators of theformula I are preferably used. These are in particular compounds of theformula I in which X.sup.⊖ is AsF₆ and very particularly SbF₆.

In this embodiment, the webs of impregnated material are as a ruleexposed to actinic radiation, particularly to UV/visible radiation,before being fed through the twin belt press.

This can be done before or immediately after impregnation or shortlybefore the actual contacting step.

The compaction pressures in step iii) are generally 1-60 bar, preferably20-50 bar: the curing temperatures are generally 50° to 250° C.,preferably 80° to 200° C. The compression period, depending on theparticular curable mixture, is generally 0.1 to 120 minutes.

Compaction pressures and temperatures are generally dependent on theparticular curable mixture used. The reactivity and state of aggregationof the particular resin/curing agent mixture, for example, aresignificant in the selection of experimental parameters.

The conditions necessary in a particular case can be selected andoptimized by an expert using the criteria given above.

Practically all epoxy resins are suitable for use as the epoxy resinwith on average at least two 1,2-epoxide resin groups per molecule.Examples of these are:

I) Polyglycidyl esters and poly-(β-methylglycidyl) esters, which arederived from compounds having at least two carboxyl groups in themolecule and epichlorohydrin or glyceroldichlorohydrin orβ-methylepichlorohydrin.

Aliphatic polycarboxylic acids can be used as compounds having at leasttwo carboxyl groups in the molecule. Examples of these polycarboxylicacids are oxalic acid, succinic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid, sebacic acid or dimerized ortrimerized linoleic acid.

Cycloaliphatic polycarboxylic acids can however also be used, forexample tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid,hexahydrophthalic acid or 4-methylhexahydrophthalic acid.

Moreover, aromatic polycarboxylic acids can be used, for example,phthalic acid, isophthalic acid or terephthalic acid.

II) Polyglycidyl ethers or poly-(β-methylglycidyl) ethers which arederived from compounds having at least two free alcoholic hydroxylgroups and/or phenolic hydroxyl groups and a suitably substitutedepichlorohydrin.

Examples of compounds having at least two alcoholic hydroxyl groups areacyclic alcohols, such as ethylene glycol, diethylene glycol and higherpoly-(oxyethylene)glycols, propane-1,2-diol orpoly-(oxypropylene)glycols, propane-1,3-diol, butane-1,4-diol,poly-(oxytetramethylene) glycols, pentane-1,5-diol, hexane-1,6-diol,hexane-2,4,6-triol, glycerol, 1,1,1-trimethylolpropane, pentaerythritol,sorbitol and polyepichlorohydrins.

Ethers of this kind can also be derived from cycloaliphatic alcohols,such as from 1,3- or 1,4-dihydroxycyclohexane,bis-(4-hydroxycyclohexyl)-methane, 2,2-bis(4-hydroxycyclohexyl)-propaneor 1,1,-bis-(hydroxymethyl)-cyclohex-3-ene.

The epoxide compounds can also be derived from mononuclear phenols, forexample resorcinol or hydroquinone; or they are based on multinuclearphenols, for example on bis-(4-hydroxy-phenyl)-methane,4,4'-dihydroxydiphenyl, bis-(4-hydroxyphenyl)-sulfone,1,1,2,2-tetrakis-(4-hydroxyphenyl)-ethane,2,2-bis-(4-hydroxyphenyl)-propane,2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane and on novolaks obtainableby a condensation reaction of aldehydes, for example formaldehyde,acetaldehyde, chloral or furfuraldedehyde, with phenols such as phenol,or with phenols which are substituted in the nucleus by chlorine atomsor C₁ -C₉ alkyl groups, for example 4-chlorophenol, 2-methylphenol or4-tert-butylphenol, or obtainable by a condensation reaction withbisphenols, as described above.

These epoxy resins also include the higher molecular weight and highermelting epoxy resins which are obtainable by so-called advancementreaction, i.e. by reacting relatively low molecular weight and lowmelting or liquid epoxy resins with polyfunctional compounds. Startingmaterials for advancement reactions of this type are, for example, lowmolecular weight diglycidyl ethers based on bisphenol, such as based onbisphenol A, which are reacted with less than the equivalent amount of abisphenol, such as bisphenol A or tetrabromobisphenol A, in a mannerknown per se to produce higher molecular weight compounds.

Reactions of this kind are known per se and are described, for example,in Kirk-Othmer "Encyclopedia of Chemical Technology", Volume 9, pp.275-276 (J. Wiley & Sons, New York 1980).

III) Poly-(S-glycidyl) compounds, particularly di-S-glycidylderivatives, which are obtained from dithiols, for exampleethane-1,2-dithiol or bis-(4-mercaptomethylphenyl)ethers.

IV) Cycloaliphatic epoxy resins, such as bis-(2,3-epoxycyclopentyl)ethers, 2,3-epoxycyclopentylglycidyl ethers or1,2-bis-(2,3-epoxycyclopentyloxy)-ethane or3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate.

However, epoxy resins may also be used in which the 1,2-epoxide groupsare bonded to different hetero-atoms or functional groups; included inthese compounds are for example the glycidyl ether-glycidyl salicylates.

If desired, a mixture of epoxy resins can be used in the curablemixtures.

In order to control the viscosity profile in stage iii) it can beadvantageous to use a modified epoxy resin in stage i), so as to obtaina higher initial viscosity and a faster increase in viscosity during thecompression moulding stage.

Thus the epoxy resin can, for example, be modified by partial reactionwith an epoxide curing agent which is effective at elevated temperature,for example an anhydride curing agent; or the epoxy resin is combinedwith a small quantity of a polyphenol, particularly of a novolak.

The quantity of modifiers is selected in such a way that the viscosityof the resin to be modified is increased, which increase is however notso big, that the initial fall in viscosity of the epoxy resin in stepiii) is suppressed.

In this embodiment a polyglycidyl ether particularly a diglycidyl etherbased on bisphenol, which may preferably be advanced if desired, is alsopartially reacted with a cyclic anhydride of a polycarboxylic acid,particularly with an anhydride of a cycloaliphatic dicarboxylic acid; inanother preferred alternative embodiment a polyglycidyl ether,particularly a diglycidyl ether based on bisphenol, which may also beadvanced if desired, is combined with a small quantity of a novolak,particularly of a phenol-formaldehyde-novolak or of acresol-formaldehyde-novolak.

A π-arene R¹ or R² is generally a non-basic heterocyclic aromatic orparticularly a carbocyclic aromatic radical, having one or more aromaticrings, and in the case of radicals with more than one aromatic ring,these may be uncondensed or condensed. These radicals may beunsubstituted or they may be substituted by non-basic radicals. π-areneR¹ or R² may be, in particular carbocyclic aromatic hydrocarbons having6 to 24 carbon atoms, particularly having 6 to 12 carbon atoms, orheterocyclic aromatic hydrocarbons having 4 to 11 carbon atoms and 1 to2 O or S atoms, where, if desired, these groups may be monosubstitutedor polysubstituted by identical or different monovalent radicals, suchas halogen atoms, preferably chlorine or bromine atoms, or C₁ -C₈-alkyl, C₁ -C₈ alkoxy or phenyl groups. Uncondensed, polynuclear π-arenegroups may be bonded directly or via bridging groups, such as --CH₂ --,--C(CH₃)₂ --, --CH═CH--, --O--, --S--, --SO₂ -- or --CO--.

Here, the alkyl or alkoxy groups may be straight chain or branched.Examples of typical alkyl or alkoxy groups are methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl andn-octyl, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, n-hexyloxyand n-octyloxy. Alkyl or alkoxy groups having 1 to 4 carbon atoms arepreferred. Preferred the substituted π-arenes are those which containone or two of the above substituents, particularly methyl, ethyl,n-propyl, isopropyl, methoxy or ethoxy groups.

Moreover R² may be an indenyl anion and particularly a cyclopentadienylanion, where these anions also may if desired be monosubstituted orpolysubstituted, particularly monosubstituted, by identical or differentmonovalent radicals such as C₁ -C₈ alkyl or C₁ -C₈ alkoxy groups. R² ispreferably an unsubstituted indenyl anion and an unsubstitutedcyclopentadienyl anion is particularly preferred.

Examples of suitable π-arenes R¹ or R² are benzene, toluene, xylenes,ethylbenzene, cumene, methoxybenzene, ethoxybenzene, dimethoxybenzene,p-chlorotoluene, m-chlorotoluene, chlorobenzene, bromobenzene,dichlorobenzene, trimethylbenzene, trimethoxybenzene, naphthalene,1,2-dihydronaphthalene, 1,2,3,4-tetrahydronaphthalene,methylnaphthalene, methoxynaphthalene, ethoxynaphthalene,chloronaphthalene, bromonaphthalene, biphenyl, stilbene, indene,4,4'-dimethylbiphenyl, fluorene, phenanthrene, anthracene,9,10-dihydroanthracene, triphenyl, pyrene, perylene, naphthacene,coronene, thiophene, chromene, xanthene, tioxanthene, benzofuran,benzothiophene, naphthothiophene, thianthrene, diphenylene oxide anddiphenylene sulfide.

Examples of anions of substituted cyclopentadienes are the anions ofmethyl-, ethyl-, n-propyl- and n-butylcyclopentadiene or the anions ofdimethylcyclopentadiene.

When a is 2, R² is preferably in each case the indenyl anion, or ifdesired the substituted indenyl anion, or particularly thecyclopentadienyl anion.

The parameter a is preferably 1. The parameter b is preferably 1.

X.sup.⊖ is preferably an anion of the formula [LQ_(m) ].sup.⊖. Q ispreferably fluorine. L is preferable As or Sb and particularly Sb.

The anion X.sup.⊖ may also be an anion of a partly fluorinated orperfluorinated aliphatic or aromatic sulfonic acid.

Anions of perfluoroaliphatic or perfluoroaromatic organic sulfonic acidsare preferably used.

Examples of these are anions of C₁ -C₈ perfluoroalkane-monosulfonicacids or of perfluorobenzene-- or perfluorotoluene-monosulfonic acid,such as CF₃ SO₃ ⁻, C₂ F₅ SO₃ ⁻, C₂ F₇ SO₃ ⁻, C₄ F₉ SO₃ ⁻, C₆ F₁₃ SO₃ ⁻,C₈ F₁₇ SO₃ ⁻, C₆ F₅ SO₃ ⁻ and CF₃ --C₆ F₄ SO₃ ⁻.

All of these anions are exceptionally weak nucleophiles.

Preferred anions X.sup.⊖ are PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻ or SbF₅ (OH)⁻.

Of these anions, AsF₆ ⁻ and SbF₆ ⁻ are especially preferred. Initiatorscontaining the anions just mentioned, in particular containing the SbF₆⁻ anion, produce particularly fast curing epoxy resin mixtures.

The compounds of the formula I can be prepared by analogy with processesknown per se. The preparation of metallocene complexes of this typecontaining complex halide anions is described for example in EP A94,915.

Deviating from the process described there, compounds of the formula Icontaining other anions may be prepared by introducing instead of ananion of a complex acid, an anion of the acid HX in a manner per se, inwhich case X.sup.⊖ is as defined further above.

A process is preferred in which the epoxy resin in step i) is adiglycidyl ether based on bisphenol, particularly a brominateddiglycidyl ether based on a bisphenol or a prepolymerized diglycidylether based on a bisphenol.

A process is particularly preferred in which the epoxy resin in step i)is a diglycidyl ether based on a bisphenol, particularly based onbisphenol A, which may if desired be advanced, which is modified with asmall quantity of a cyclic anhydride of a polycarboxylic acid,particularly of an anhydride of a cycloaliphatic dicarboxylic acid.

A process which is also particularly preferred, is that in which theepoxy resin in step i) is a diglycidyl ether based on a bisphenol,particularly based on bisphenol A, which may if desired be advanced, andwhich is used together with a small quantity of a novolak, particularlyof a cresol-formaldehyde-novolak or of a phenol-formaldehyde-novolak.

A process is further preferred, in which the initiator has the formulaIa

    [R.sup.3 Fe.sup.II R.sup.4 ].spsp.⊕X'.sup.⊖    (Ia),

in which R³ is a stilbene radical or is a benzene or naphthalene radicalhaving one or two C₁ -C₄ alkyl or C₁ -C₄ alkoxy substituents,particularly a cumene or a methylnaphthalene radical, R⁴ is anunsubstituted cyclopentadienyl anion and X'.sup.⊖ is selected from thegroup comprising AsF₆ ⁻ and SbF₆ ⁻.

A process is particularly preferred, in which in step iii), a compactionpressure of 20-50 bar is applied for 1-45 minutes at a temperature of80° to 200° C., particularly in the range 100° to 200° C.

A process is very particularly preferred in which glass fabric or paperis used as the fibrous substrate in step i).

As already described further above, the cured laminates prepared by thisprocess have improved final properties in comparison with conventionallyprepared products.

The invention therefore also relates to the laminates which can beobtained by means of the above process.

The invention also relates to the use of the compounds of the formula I,defined further above, for preparing laminates, preferably based onepoxides.

The curable composition used in step i) may also contain furtheradditives. These can be additives with which the final properties of thecured laminates and/or the processing properties of the mixture aremodified.

Examples of such additives are fillers or extenders, such as chalk,talc, kaolin, mica, gypsum, titanium dioxide, powdered quartz, aluminiumoxide, cellulose, alumina, ground dolomite, wollastonite, kieselguhrhaving a large specific surface area (obtainable under the trade nameAerosil), alumina modified with long chain amines (obtainable under thename Bentone), powdered polyvinyl chloride, polyolefines oraminoplastics, and metal powders, such as copper, silver, aluminium oriron powder, flame retardants, such as antimony trioxide; colorants,such as pigments or dyes; light stabilizers to improve the UV-resistanceof the finished laminate; release agents, in order for example toseparte the individual layers prepared in step i) at an intermediatestage, such as release films, film-forming paints or waxes; thixotropicagents, such as highly dispersed silic; reactive diluents, such asphenylglycidyl ether or cresyl glycidyl ether, butanediol diglycidylether or hexahydrophthalic acid diglycidyl ether; or inert diluents, forpreparing, for example, impregnation solutions from highly viscous orsolid epoxy resin mixtures, such as chlorinated aliphatic or aromatichydrocarbons, e.g. methylene chloride, trichloroethane,tetrachloroethane, chlorobenzene, or such as aromatic hydrocarbons, suchas toluene or xylene, or such as aliphatic ketones, such as acetone ormethyl ethyl ketone.

The laminates which are obtainable according to the invention areparticularly useful for preparing printed circuit boards and insulatingmaterials.

The following examples illustrate the invention.

EXAMPLE 1

A solution is prepared from 500 g of brominated technical gradediglycidyl ether based on bisphenol A (epoxide content: 2.30equivalents/kg; bromine content: 19.7% by weight), dissolved in methylethyl ketone, and 2.0 g (η⁶ -isopropylbenzene) (η⁵-cyclopentadienyl)iron(II) hexafluoroantimonate (abbreviated to"photoinitiator I"). The concentration of this photoinitiator is 0.5percent by weight based on the solid epoxy resin in the solution.

Webs made from glass fabric (weight per unit area 200 g/m²) areimpregnated with this solution; the impregnated glass fabric is allowedto drain at room temperature for a few minutes, before it is freed fromsolvent in a vented oven at 150° C. for 5 minutes. The webs which havebeen freed from solvent are irradiated for 120 seconds using a 5,000Watt high pressure mercury vapour lamp, the distance between the glassfabric and the lamp being about 40 cm. The fabric is then cut intopieces of 15×15 cm. 8 of these pieces at a time are processed togetherin a heatable press to a laminate; in doing this, initial conditionsapplied are a pressure of 40 bar operating for 15 minutes at 80° C. andsubsequently a pressure of 40 bar operating for 10 minutes at 180° C.The glass transition temperature of the finished laminate is 153° C.

EXAMPLES 2-4

As described in Example 1, glass fabric-reinforced laminates areprepared from the epoxy resin according to Example 1 and photo-initiatorI, the amount of which is given in percent by weight, based on solidepoxy resin, in Table 1. This table also contains information about thedrying period and drying temperature, the exposure time, and thecompression cycle used, and the glass transition temperature achieved.

EXAMPLE 5

As described in Example 1, a laminate is prepared from photoinitiator Iand a brominated technical grade diglycidyl ether based on bisphenol A(epoxide content: 2.8 equivalents/kg; bromine content: 20.3% by weight)dissolved in methyl ethyl ketone. The amount of photoinitiator aspercent by weight of the solvent-free resin, drying period and exposuretime, compression moulding conditions and the glass transitiontemperature of the finished laminate are given in Table 1.

                                      TABLE 1                                     __________________________________________________________________________          Amount of             Compres-                                                                            Tg                                                photo-initiator       sion cycle                                                                          of                                          Example                                                                             I based on                                                                            Drying in                                                                              Exposure                                                                           pressure:                                                                           lami-                                       No.   solid resin                                                                           vented oven                                                                            time 40 bar                                                                              nate                                        __________________________________________________________________________    2     1.0     5 min/150° C.                                                                   60 sec.                                                                            15'/90°                                                                      +153° C.                                                         20'/170°                                   3     1.0     5 min/150° C.                                                                   15 sec.                                                                            15'/130°                                                                     +154° C.                                                          5'/180°                                   4     0.5     5 min/150° C.                                                                   30 sec.                                                                             5'/130°                                                                     +150° C.                                                         10'/180°                                   5     1.0     5 min/150° C.                                                                   60 sec.                                                                            15'/90°                                                                      +182° C.                                                         20'/180°                                   __________________________________________________________________________

EXAMPLE 6

6.0 g "photoinitiator I" are dissolved in 594 g of liquid brominatedsolvent-free diglycidyl ether based on bisphenol A (epoxide content: 4.3equivalents/kg; bromine content: 20.5% by weight) at room temperature.This resin is used to impregnate webs of glass fabric (200 g/m² weightper unit area), the soaked glass fabric is allowed to drain for a fewminutes before it is irradiated with UV light for 120 seconds asdescribed in Example 1. The soaked web is then cut into pieces of 15×15cm; 8 of these pieces at a time are laid on top of one another, andprocessed in a heatable press to produce a laminated moulding, for whichthey are subjected to a pressure of 20-30 bar at 180° C. for 20 minutes.The glass transition temperature of the finished laminate is 170° C.

EXAMPLE 7

10.0 g (η⁶ -1-methylnaphthalene)(η⁵ -cyclopentadienyl)iron(II)hexafluoro-antimonate (abbreviated to "photoinitiator II") are added to612.5 g of the brominated epoxy resin according to Example 1. Theconcentration of this photoinitiator is 2 percent by weight based onsolid epoxy resin. Webs of glass fabric (weight per unit area 200 g/m²)are soaked in this solution, the impregnated fabric is allowed to drainfor about 5 minutes at room temperature, before it is freed from solventin a vented oven at 150° C. over a period of 5 minutes. The solvent-freewebs are cut into pieces 15×15 cm in size.

8 of these pieces at a time are placed together in a press andcompression moulded to a laminate, initially at a pressure of 20 bar for10 minutes at 130° C., and subsequently at a pressure of 50 bar for 20minutes at a temperature of 150° C. The glass transition temperature ofthe laminate is 142° C.

EXAMPLE 8

12.0 g "photoinitiator II" are dissolved at room temperature in 588 g ofliquid solvent-free epoxy resin according to Example 6. Webs of glassfabric (200 g/m² weight per unit area) are impregnated with this resin;the soaked fabric is allowed to drain for a few minutes, before it iscut into pieces of 15×15 cm. 8 of these pieces at a time are placedtogether in a press and compression moulded to a laminate; initially apressure of 20 bar is applied for 5 minutes at 150° C., and subsequentlya pressure of 40 bar is applied for 10 minutes at 180° C. The glasstransition temperature of the laminate thus obtain is 169° C.

EXAMPLE 9

A solution is prepared from 915 g of a mixture, dissolved in methylethyl ketone, of brominated technical grade diglycidyl ether based onbisphenol and a small quantity of the glycidyl ether of1,1,2,2-tetrakis-(4-hydroxyphenyl)-ethane (epoxide content 2.34equivalents/kg; bromine content 18.9%) and 3.2 g "photoinitiator I"; theconcentration of this photoinitiator is 0.5 percent by weight based onsolid epoxy resin in the solution. Glass fabric-reinforced laminates areprepared as described in Example 1. Drying period and exposure time,compression moulding cycle and glass transition temperature T_(g)achieved are given in Table 2.

EXAMPLE 10

A solution is prepared from 900 g of a brominated technical gradediglycid ether based on bisphenol A (epoxide content 1.86equivalents/kg; bromine content 22.1%), dissolved in methylethyl ketone,and 3.15 g "photoinitiator I"; the concentration of the initiator is 0.5percent by weight, based on solid epoxy resin. Glass fibre-reinforcedlaminates are prepared from this solution as described in Example 1.Drying period and exposure time, compression moulding cycle and glasstransition temperature achieved are given in Table 2.

EXAMPLE 11

A solution is prepared from 1,000 g of a brominated technical gradediglycidyl ether based on bisphenol A (epoxide content 2.55equivalents/kg; bromine content 21.5%), which contains a small amount ofa glycidylized novolak, dissolved in methylglycol and methyl ethylketone, and 7.5 g "photoinitiator I"; the concentration of the latter is1.0% based on solid resin in the solution. A glass fibre-reinforcedlaminated is prepared from this solution as described in Example 1;drying period and exposure time, compression moulding cycle and glasstransition temperature are given in Table 2.

EXAMPLE 12

A solution is prepared comprising 800 g of a brominated technical gradediglycidyl ether based on bishphenol A (epoxide equivalent 1.88equivalents/kg; bromine content 19.5%), dissolved in methyl ethylketone, and a small quantity of a phenolic novolak and 3.2 g"photoinitiator I"; the concentration of the latter is 0.5% based onsolid resin in the solution. A glass fibre-reinforced laminate isprepared from this solution as described in Example 1. Drying period andexposure time, compression moulding cycle and glass transitiontemperature are given in Table 2.

EXAMPLE 13

A solution is prepared from 800 g of a brominated technical gradediglycidyl ether based on bisphenol A and tetrahydrophthalic anhydride(epoxide equivalent 1.83 equivalents/kg; bromine content 19.4%),dissolved in methyl ethyl ketone, and 3.2 g "photoinitiator I"; theconcentration of the latter is 0.5% based on solid resin in thesolution. A glass fibre-reinforced laminate is produced from thissolution as described in Example 1. Drying period and exposure time,compression moulding cycle and glass transition temperature are given inTable 2.

EXAMPLE 14

A solution is prepared from 800 g of a brominated technical gradediglycidyl ether based on bisphenol A and hexahydrophthalic anhydride(epoxide equivalent 1.83 equivalents/kg; bromine content 19.5%),dissolved in methyl ethyl ketone, and 3.2 g "photoinitiator I"; theconcentration of the latter is 0.5% based on solid resin in thesolution. A glass fibre-reinforced laminate is compression moulded usingthis solution as described in Example 1. Drying period and exposuretime, compression moulding cycle and glass transition temperature aregiven in Table 2.

EXAMPLE 15

1.0 g "photoinitiator I" are dissolved in 400 g of liquid, solvent-free3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate. Webs ofglass fabric (200 g/m² weight per unit area) are impregnated with thisresin and the glass fabric is allowed to drain for a few minutes beforeit is irradiated for 15 seconds with UV light. Subsequently 8 pieces,about 15×15 cm in size, at a time of the soaked fabric are laid one ontop of another and processed in a heatable press at a pressure of 20-30Kp/cm² for 15 minutes at 170° C. to give a laminate, which has a glasstransition temperature of 135° C.

EXAMPLE 16

Using the solution mentioned in Example 10, webs of glass fabric areimpregnated and dried as described in Example 1. The impregnated websare passed under a UV lamp (Fusion-D-lamps, 120 W/cm) at a speed of 7m/minute. Subsequently the exposed prepregs are cut up and compressionmoulded as in Example 1. Drying period and exposure time, compressionmoulding cycle and glass transition temperature T_(g) achieved are givenin Table 2.

EXAMPLE 17

A solution is prepared from 375 g of the epoxy resin mentioned inExample 1 and 0.75 g "photoinitiator I" and 3.0 g (η⁶ -stilbene) (η⁵-cyclopentadienyl)iron(II) hexafluorophosphate, i.e. 0.25% and 1.0%based on solid resin in the solution. Glass fabric-reinforced laminatesare prepared as described in Example 1. Drying period and exposure time,compression moulding cycle and glass transition temperature T_(g)achieved are given in Table 2.

EXAMPLE 18

A solution is prepared from 563 g of the epoxy resin mentioned inExample 1 and 2.25 g (η⁶ -stilbene)(η⁵ -cyclopentadienyl)iron(II)hexafluoro-antimonate; the concentration of the initiator is 0.5% basedon solid epoxy resin. This solution is used to prepare a glassfibre-reinforced laminate as described in Example 1, and the dryingperiod and exposure time and the compression moulding conditions andglass transition temperature are given in Table 2.

                  TABLE 2                                                         ______________________________________                                        Ex-   Drying in   Exposure Compression moulding                               ample the vented  time     cycle*.sup.) Tg                                    No.   oven        (sec.)   Time  Temperature                                                                          (°C.)                          ______________________________________                                         9    5 mins/140° C.                                                                     30       15'/170° C.                                                                         150                                   10    5 mins/140° C.                                                                     60       10'/180° C.                                                                         143                                   11    5 mins/150° C.                                                                     120      15'/100° C.                                                                         153                                                              +20'/180° C.                                12    5 mins/170° C.                                                                     30       10'/180° C.                                                                         144                                   13    2 mins/190° C.                                                                     30        3'/200° C.                                                                         139                                   14    5 mins/150° C.                                                                     30        3'/200° C.                                                                         141                                   16    5 mins/140° C.                                                                     --       10'/170° C.                                                                         142                                   17    2 mins/190° C.                                                                     30       15'/180° C.                                                                         139                                   18    5 mins/150° C.                                                                     30       15'/170° C.                                                                         144                                   ______________________________________                                         *.sup.) Pressure 20-30 (bar)                                             

We claim:
 1. A laminate obtained from a process comprisingi) contactinga fibrous substrate with a curable mixture consisting essentially of atleast one epoxy resin having on average at least two 1,2-epoxide groupsper molecule and, as initiator, at least one compound of formula I

    [R.sup.1 (Fe.sup.II R.sup.2).sub.a ].sup.ab.spsp.⊕ ab.[X].spsp.⊖(I)

in which a and b are independently of one another 1 or 2, R¹ is acarbocyclic aromatic hydrocarbon having 6-24 carbons atoms which isunsubstituted or substituted one or more times with halogen, C₁ -C₈alkyl, C₁ -C₈ alkoxy or phenyl; or R¹ is a heterocyclic aromatichydrocarbon having 4-11 carbon atoms and 1 to 2 O or S atomsunsubstituted or substituted one or more times with halogen, C₁ -C₈alkyl, C₁ -C₈ alkoxy or phenyl; R² is a carbocyclic aromatic hydrocarbonhaving 6-24 carbons atoms which is unsubstituted or substituted one ormore times with halogen, C₁ -C₈ alkyl, C₁ -C₈ alkoxy or phenyl; or R² isa heterocyclic aromatic hydrocarbon having 4-11 carbon atoms and 1 to 2O or S atoms unsubstituted or substituted one or more times withhalogen, C₁ -C₈ alkyl, C₁ -C₈ alkoxy or phenyl; or R² is an indenyl or acyclopentadienyl anion unsubstituted or substituted with C₁ -C₈ alkyl orC₁ -C₈ alkoxy; X⁻ is an anion of a partly fluorinated or perfluorinatedaliphatic or aromatic sulfonic acid or an anion [LQ_(m) ]⁻ wherein L isP, As or Sb, and Q is fluorine or a mixture of fluorine and hydroxyl, mcorresponds to a value which exceeds the valence of L by one; ii)preparing a laminated sequence from at least two layered materials whichare to be bonded together, at least one of which is a layer according tostep i) wherein practically no preliminary crosslinking occurs; iii)placing the laminated sequence in a compression mold; iv) compressionmolding the laminated sequence wherein pressure and temperature areselected in such a way that a liquid matrix is present at the beginningof this step in which an initial fall in viscosity is produced so thatentrained gases can escape from the laminated sequence; and v)crosslinking the compression molded laminate sequence such that the risein viscosity is carried out so quickly that the resin which flows outdoes not bind the compression mold.
 2. A laminate according to claim 1wherein an irradiation step ia) is incorporated before step ii), inwhich the compound of the formula I is exposed to actinic irradiationfor activation.
 3. A laminate according to claim 1 wherein the epoxyresin in step i) is a diglycidyl ether based on a bisphenol.
 4. Alaminate according to claim 1 wherein the initiator has the formula Ia

    [R.sup.3 Fe.sup.II R.sup.4 ].spsp.⊕X'.sup.⊖    (Ia)

in which R³ is a stilbene radical or is a benzene or naphthalene radicalhaving one or two C₁ -C₄ alkyl or C₁ -C₄ alkoxy substituents, R⁴ is anunsubsituted cyclopentadienyl anion and X'.sup.⊖ is selected from thegroup comprising consisting of AsF₆ and SbF₆.
 5. A laminate according toclaim 1, wherein the fibrous substrate of step i) is glass fabric orpaper.
 6. A laminate according to claim 1, wherein the epoxy resin is adiglycidyl ether based on bisphenol which is modified with a cyclicanhydride of a polycarboxylic acid or a high molecular weight productmade by reacting a diglycidyl ether based on bisphenol with less than anequivalent amount of a bisphenol which is modified with a cyclicanhydride of a polycarboxylic acid.
 7. A laminate according to claim 6,wherein the bisphenol is bisphenol A and the cyclic anhydride of apolycarboxylic acid is an anhydride of a cycloaliphatic dicarboxylicacid.
 8. A laminate according to claim 6 further comprising a novolac.9. A laminate according to claim 8, wherein said novolac is acresol-formaldehyde-novolac or a phenol-formaldehyde-novolac.